From the webpage:
Do you have the next big story? Want to share it with The New York Times? We offer several ways to get in touch with and provide materials to our journalists. No communication system is completely secure, but these tools can help protect your anonymity. We’ve outlined each below, but please review any app’s terms and instructions as well. Please do not send feedback, story ideas, pitches or press releases through these channels. For more general correspondence visit our contact page.
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The New York Times offers five (5) ways that offer some protection to your anonymity, depending upon your skill and what you leak.
When you leak, request posting of the raw leak within some reasonable period of time.
Government data belongs to the people, not its publisher.